Removing the superfluous use before library on the first line of your code and using VHDL revision -2008 your code analyzes and elaborates (evaluating a port of mode out is possible in -2008). Please provide a minimal reproducible example including complete error message and identifying the operation your tool was performing, the problem isn't guaranteed reproducible from your question as is.
– user1155120Feb 5 at 20:05

2 Answers
2

You can't read the value of an out in VHDL revisions prior to VHDL-2008. The usual way to get around this is to have an internal copy of your output, and use that internal copy when you need to get its value: